Monte Carlo (MC) simulation is a powerful tool for modeling light distribution in tissue. We have used MC simulations to model the effect of tissue turbidity to the incident excittaion light and the resulting fluorescence light. Tissue optical parameters as absorption and scattering are being varied and the reflectance and fluorescence signals escaping from the tissue surface are calculated as a function of tissue optical characteristics. These calculations have provided information required in determining the distortion of the observed signals from tissue, due to scattering and absorption. This information is very critical for the development of tissue fluorescence models which will be the basis of new diagnostic algorithms, and it is also very useful in spectral probe design.